Paul Merton: 'Comedy is as difficult as playing the violin.’
Photograph: David Levene for the Guardian

In my experience there are two types of comedian who, no matter how funny they may be on stage, you wouldn't really want to meet in real life. There's the cliche of the curmudgeonly comic – grouchy, aloof, a bit passive aggressive – and there's the one who can't switch off, and craves laughter like you or I need oxygen. When I told people I was going to meet Paul Merton, everyone had him down as a classic case of the former – and to be honest, that was my fear too.

Merton's comic persona can be pretty devastating towards others' stupidity, which is terrifically funny to watch, but presumably not quite as fun to find oneself on the receiving end of. And my worry was that while I quite enjoyed his new documentary series, I couldn't think of a single question to ask about it. It's a history of the early days of Hollywood, and if old film is your thing then I'm sure it's brilliant – but it's not really mine, and a BBC press officer had been making matters worse by sending slightly ominous emails, specifying scenes which he claimed Merton was "particularly" keen for me to see. Oh God, was I going to be quizzed on them?

It takes less than a minute to forget all these fears. For a start, the press officer is politely but firmly waved away by Merton, who casts a puzzled glance at the departing figure and asks, "Who was he anyway?" Then he bursts out laughing – and keeps laughing on and off for the best part of two hours. In fact I've seldom met anyone who seems happier in their own skin – even if he is dressed like a runaway from the circus, in a big charcoal suit over a psychedelic swirl of multicoloured silk shirt. "Ah, well I've got a sort of clothes blindness," he admits cheerfully.

So the cliche of the curmudgeon is wide of the mark – and so, happily, is that of the needy performer who has to turn every conversation into a standup routine, and everyone around him into an audience. Merton has the most exuberant enthusiasm for humour, but in his company you feel as if he's willing you to be funny too, and he's one of the few comics I've met who seems genuinely happiest when sharing the jokes. He has a formative early memory of hearing audience laughter, as a five-year-old at a clown show, and being "absolutely knocked out by it". But when I ask why the sound affected him so profoundly, he doesn't say anything about the epiphany of humour's power, which so many comedians cite. "Oh," he says intensely, "it was just – it was just – it was just joyful!"

Almost half a century later, Merton still seems just as intoxicated by the joy of it. Now 53, he's been making us laugh ever since the mid-80s, first as a standup at the Comedy Store, then on Whose Line Is It Anyway, before joining Radio 4's Just a Minute in 1988, and BBC1's Have I Got News For You in 1990. Success, of course, has a habit of looking inevitable with hindsight, and it's impossible to imagine Just a Minute or Have I Got News For You without Merton. But the producer who first hired him for Just a Minute admitted to Merton, when they were reunited recently, that at the time he'd feared he was booking "some oik".

It's hard to remember now, but Merton first emerged as a member of the alternative comedy generation – edgy, impudent, and as Ben Elton would say, "a bit poli'ical". But his career has in fact never been particularly political, and his humour has always sailed closer to surrealism than iconoclasm, so class consciousness was the last thing I was expecting to come up. When Merton recalls his early life, however, class is the defining theme of his experience.

Merton had been playing Just a Minute by himself since he was eight years old. "Kids love it because it's very easy to understand, and very difficult to play – which is a brilliant combination." But he grew up in a working-class home, in a council house in Fulham, failed his 11-plus, and left school at 18 – "university never even crossed my mind" – to go and work in an employment office. He spent the early 80s living in south London bedsits, flat broke and lonely, working on his craft as a comedian.

"I didn't have a telly – the radio was my only entertainment thing – so I'd make a little library of Just a Minute tapes to play when I was going to sleep at night. I heard one of the episodes recently on BBC7," he laughs, "and I knew every word of it." By the late 80s Merton was making a name for himself in improvisation on Whose Line Is It Anyway? – so when Just a Minute regular Kenneth Williams died in 1988, Merton wrote to the show's producer, asking to appear on the show.

"He phoned me up in my bedsit, and said," – and Merton puts on a posh voice – "'Now you know what sort of show it is, don't you?' Yes, I said, I do. 'Well, don't swear. And what will you be wearing?' I think he thought he was booking Sid Vicious or something."

Merton is laughing as he recalls the conversation, and seems anxious at first to make light of it. "Well, class is awkward, isn't it? Am I allowed to call myself working-class now? Because obviously I'm now very rich. But the phrase 'working-class' is the phrase I grew up with – and so much of the working-class thing is about thinking you're not allowed to do stuff." The more he talks, the clearer it becomes that class was no joke for him as a young man – and still isn't, even now.

"When I started off as a comic, aged 23 or 24, I remember looking at another comedian who used to read the Guardian, and thinking to myself: 'God, I wish I read the Guardian.' And then I thought: 'Hang on a minute, just go and buy it. Yes I can!' But actually I had to get over that barrier. It's just like I used to say: 'Oh, I wish I liked jazz, jazz seems to be something you could really get into.' It's bizarre, isn't it?"

But then he starts to look a little uneasy. He can't bear, he says, to look as if he might have a chip on his shoulder – "cos that's what gets thrown at you – as if to complain about your position is somehow not allowed. And there's nothing about my life I can resent now. But how the working class are sometimes portrayed is – well, galling." I ask for an example, and he hesitates - but then, after a long sigh:

"Well you know, someone like Boris Johnson, he's done Have I Got News for You several times, but Boris doesn't know anything about – well, Boris is just not from the world where you think: 'I've got 36p in my pocket and the giro doesn't arrive for another two days, what am I going to do?' But that used to be my world."

Then he tells a story about standing in a park next to Fulham's football ground with his dad when he was only eight or nine. He looked across the Thames, and asked his father what was on the other side of the river. And his father told him there was nothing there; that he couldn't go over there.

"Then when I got to the age of about 19, I wondered if something was there. And this is going to sound ludicrous, but it's as it was. I thought I'll go and have a look. So I got off the bus, and instead of going over the bridge I went along the other side of the bank. And there was a rowing club, and people rowing; people from Cambridge, and Barclays, and stuff. And I felt so inhibited by them, I couldn't go any further on. I had to go back. These rowers and stuff – this is it, this is the thing – not feeling you fit in. I didn't feel as if I fitted in. Feeling that you shouldn't be there. That somebody's going to tell you off. That you're in the wrong place. And I realised I'd been told something at the age of 10, that you can't go there – that it's not for you. And I just believed it. So when people say: 'Oh what's wrong with the working class? All they've got to do is this and that.' Well no, it's not as easy as that."

He breaks off, looking slightly apologetic. "I'm just trying to talk about this without sounding as if I've got a grudge, cos there is no grudge. I hope this isn't sounding like a terrible sob story, I don't mean it to be at all."

It was comedy that changed everything for him. "When I started performing, I never felt: 'Oh that person's far superior to me because of their class.' Cos comedy doesn't come into that, nobody ever says the middle classes are instinctively funny or anything like that. You're all in the dressing room together, and nobody says: 'You'd better go first cos you've got a private education.'"

When Merton launches into one of his surreal comic riffs on Just a Minute or Have I Got News For You, it's tempting to think him gifted with a kind of genius that transcends not just class but anything prosaic enough to be quantifiable. I've always wondered whether he's thinking furiously about what to say next, or has entered something closer to a state of trance, in which he's as surprised as anyone to hear what comes out of his mouth next.

"Well it's not a trance or a daze; that's not quite right. How can you describe it? There's a phrase athletes use – 'in the zone' – and you can't make it happen, you can't force it. But sometimes you just let yourself go, and I don't know where it's coming from." Does it feel more as if he's channelling something than creating it? "Yes, that's what I'm hesitating to say, I suppose," he agrees, looking slightly bashful.

But just as athletes don't find themselves in the zone by magic, Merton insists that whatever comic gift he may have can be attributed to decades of study of comedy as a discipline.

"I remember being fascinated by the very nature of comedy from the age of 10; why is this funny, and that isn't? What's the difference between rhythm and timing? In comedy it doesn't look like there's an art going on; it should look as if it's easy, cos there shouldn't be a sense of strain. But it is as difficult as playing the violin; there's a skill to be learned, there's a timing, there's a projection, there's how you sit, eye contact, how much room you give people."

To this day he still performs improv every Sunday at the Comedy Store, and insists – though I'm not quite sure I believe him – that anyone could learn how to do it if they practised enough. There are rules, and he cheerfully admits to being very old-school about treating it as a discipline.

"I looked at longevity in show business when I was about 13, and the people who seemed to have longevity were the ones who'd spent quite a bit of time learning about what they were doing before they made it. You know, Charlie Chaplin, Buster Keaton, the Marx brothers – they knew what they were doing, they weren't flash-in-the-pan overnight successes. They grew, and they built, and they sustained."

Does he feel that he's now seeing young comedians achieve overnight fame without, in his terms, doing enough hard work? "Um – I don't know," he says vaguely, sounding suspiciously diplomatic. "I really don't take any interest at all in contemporary comedy." In fact, it turns out that he's never even seen most successful contemporary acts – not Gavin and Stacey, nor Peep Show, nor The Inbetweeners. "Nope," he apologises, "afraid not." What about Miranda Hart?

"Yes, I think that's it. One of the things that basically never changes is that people like laughing at people falling over. Look at You've Been Framed! Every week it's children being carried out of playgrounds with serious head injuries while we all laugh and clap. But she does it with real skill, she has the most amazing physicality, and it's unusual for a woman to have that much confidence in it."

It was this sort of old-fashioned concern for attention to discipline and detail that made Merton fall in love with early Hollywood. His three-part documentary series is an authoritative and entertaining narrative, not only presented by him, but written and directed as well – and he says he'd quite happily never perform again if he could spend the rest of his career directing. "For ages," he grins, "I'd fallen into that trap of saying, 'Oh yes, I'm going to direct a film' – but not actually doing it. Then I suddenly realised one thing that distinguishes directors from other people is that they actually direct! And now I love it, I just love it. It's something to really get your teeth into."

His co-writer on the series is his third wife and fellow comic improviser, Suki Webster. Merton was married to the actor Caroline Quentin in the 90s, but it was his second marriage that many more may remember, because he wed actor Sarah Parkinson just three months before she died in his arms of breast cancer in 2003. Throughout her illness Merton cut a heartbreaking figure, heavily bearded, and bringing organic juices to her bedside following her decision to decline chemotherapy.

I suspect it was her death that contributed to a public impression of Merton as a glum, even tragic soul. But it was comedy again that rescued him, for within weeks he was seen in the audience of the Comedy Store, where he says he found profound comfort in the sound of people laughing. He seems so happy today that when he talks of his frustration at not having more time to make and direct films, I suggest he could always stop doing Have I Got News for You, or stop doing Just a – but before the words are even out of my mouth he interrupts.

"Ooh no, I could never stop doing Just a Minute," he exclaims, looking appalled. "Oh God, no. I still can't believe I'm in it."